Task Coach is a free, Open Source to-do manager. It grew out of frustration that other programs do not handle composite tasks well. In addition to flexible composite tasks, Task Coach has grown to include prerequisites, prioritizing, effort tracking, category tags, budgets, notes, and many other features. However, users are not forced to use all these features; Task Coach can be as simple or complex as you need it to be. Task Coach is available for OS X, Windows, and GNU/Linux; and there is a companion iOS app.